Obs. [In med. or mod.L.: no Lat. or Gr. derivation is known.] A term of Paracelsian Chemistry, used in various senses: e.g., ‘the quintessence of a thing; the reunion of different principles, as oil, salt, and spirit, by long digestion; the product of the detonation of nitre with another substance’ (Mayne, Expos. Lex.). According to Rolfenkius, meaning ‘compound mineral spirits.’ (Syd. Soc. Lex.)
1650. French, New Light Alchymie, Gloss., Clissus is the occult vertue of things returning from whence they came, as the vertue of an hearb into the root in Autumne.
1682. Bruno, Castelli Lex, renovatum, s.v.
1708. J. Harris, Lex. Techn., Clyssus, among some Chymists, is a long Digestion and Union of Oily Spirits (especially Mineral ones) together, in order to make a Composition or accurate Mixture of them…. Sometimes for a Medicine made of the most active and energetical Parts of any Ingredients.
1741. Chambers, Cycl., Clyssus, in Chymistry … consisting of the most efficacious Principles of any Body, extracted, purify’d, and then re-mixed.
1767. Woulfe, Distil., in Phil. Trans., LVII. 534. The vapours which arise in the deflagration of nitre, with charcoal, antimony, &c., commonly called Clyssus, are very hard to condense.
1826. Henry, Elem. Chem., I. 540. Nitrate of potassa is rapidly decomposed by charcoal at a high temperature…. The products of this combustion … are carbonic acid and nitrogen gases. Part of the carbonic acid also remains attached to the residuary alkali, and may be obtained from it on adding a stronger acid. This residue was termed, by the old chemists, clyssus of nitre.
